


Errare Diabolicum Est

by Kangoo



Series: Miscellaneous Warcraft Stuff [7]
Category: Warcraft - All Media Types, World of Warcraft
Genre: Alternate Universe - Canon Divergence, Chronically-late-to-official-functions!Illidan, Crack, Demon Summoning, Good lord I love emdashes, Guest Starring: Kael'thas enormous crush, Illidan Has No Chill, Kael'thas Has Friends, Kael'thas doesn't take shit from anyone, Kael'thas is a big nerd, M/M, Peace Summits AU
Language: English
Status: Completed
Published: 2017-10-08
Updated: 2017-10-08
Packaged: 2019-01-10 16:31:16
Rating: Teen And Up Audiences
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 3,144
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/12303093
Author URL: https://archiveofourown.org/users/Kangoo/pseuds/Kangoo
Summary: Kael'thas tries his hand at demon summoning. He summons Illidan instead.





	Errare Diabolicum Est

**Author's Note:**

> ¯\\_(ツ)_/¯
> 
> Unbeta'd, not proofread, written at 4 am, don't hesitate to tell me if you see a mistake!

Rommath leans, touching the bare skin on his arm where his wounds used to be. He can still feel the beginning of a headache — an inescapable consequence of too much magic in too little time — but apart from that, he’s as healthy as can be.

 

In front of him, Kael’thas sighs and sags in his chair, pushing his hand through his long hair.

 

“Is there anything you can’t do?” 

 

The king huffs a laugh and shrugs. “I don’t know, cooking? Winning this war? Summoning demons?” 

 

“You cook better than Lor’themar—” Rommath ignores the muttered 'a murloc can cook better than Lor’themar’ and continues, “And you’ve beend doing a descent job at stopping Jaina and Sylvanas from tearing each other’s throat, which is _definitely_ helping the war effort. Now, if only you could become a warlock...”

 

“As if we need _more_ demons,” Kael’thas says, but the realization that there’s magic he cannot do appears to annoy him.

 

Rommath ducks his head to hide his grin in his mask. 

 

\--

 

So maybe Kael’thas Sunstrider, crown prince of the sin’dorei, is a massive nerd. And maybe he loathes to leave a school of magic untried.

 

To each their faults.

 

It takes him a month to find the time, between the war against the Legion and his kingly duties, to study fel magic until he’s confident enough in his abilities to try his hand at summoning and binding a demon.

 

(It would have taken at the _least_ a year of non-stop studying for anyone else to get there but if there’s anything true about Kael’thas, it’s that he’s a bit of a genius.)

 

And then it’s another week before he finds a single free evening in his schedule to actually _do_ the summoning. The preparations take a little more time than he expected: he stumbles in his quarters at sunset (fresh out of five consecutive hours of peace summit, because for some reason Silvermoon couldn’t stay free of those for long) and when he stands above the finished summoning circle, the moon is high in the sky.

 

Kael’thas yawns, pops his back, and wonders if he has the time to grab a bite before he gets to the whole ‘dragging a creature from the void into Azeroth’ thing. 

 

Well, he can always do that after. There’s no time like the present for possible disasters, after all.

 

The ritual he’s using doesn’t come from any of the ‘So you want to be a warlock’ books he managed to get his hand on. Being a warlock is all about the mutual pact between summoner and demon: the creature offers its powers in exchange for a bit of the summoner’s magic and life-force. Warlocks tend to live short lives because of it and, because Kael’thas doesn’t feel like selling a part of his soul to the Legion just for shits and giggles, he’s decided to use his own ritual.

 

So he’s hungry, tired, and about to summon a demon using a highly modified, one-hundred percent original ritual he scribbled on spare pieces of paper during meetings. This might just be the worst idea he ever had.

 

(And he almost joined Illidan on his roaring rampage of revenge: that’s how bad it is.)

 

A snap of his fingers and candles are set alight, illuminating the room with a golden glow that can barely hides the green light of Argus that spills through the windows.

 

(Anything having to do with Illidan is a bad idea: it has been proven again and again in the last decade.)

 

Kael’thas draws the blade of his dagger over the palm of his hand and holds it over the circle, careful not to step in it as drops of blood fall on the chalk lines.

 

(Although the man _does_ have a few good points.)

 

He’s just as careful to contain his yawn as he intones the words that will open the rift to another dimension— or whatever it does, he can’t quite remember right now.

 

Or he _could_ , but he won’t, because he’s tired and also frustrated to tears, which in him translates to trying dangerous experimental magic as a way to vent.

 

(Like, the destruction of the Legion by any mean necessary? Kael’thas can get behind that. It’s unethical but it’s efficient, too, and they’re too desperate to complain about it. He would do the same for his people — almost did, if not for Lor’themar swift reaction.)

 

He utters the last words and it feels like the world stretches and tugs like a rubber band, before snapping back into place in the same way. The light of the candles flare in a flash of bright green flames, twisting around a jagged line of absolute darkness in the center of the circle so that it is the only thing visible. Kael’thas takes half a step back and blinks rapidly, trying to rid his eyes of the afterimage.

 

When his sights clears, it is to see a dumbfounded demon hunter standing in the middle of the summoning circle.

 

“What... the _fuck_ ,” Illidan says, in the perfect calm of someone about to snap and kill someone if looked at the wrong way, at the exact same time as Kael’thas says,

 

“ _How_ in _hell_ —”

 

They both fall quiet and wait in awkward silence for a second before Illidan waves a hand and says, oddly polite in that peculiar way of his that suggests eternal suffering, “Go on.”

 

“That’s not what this ritual was supposed to do _at all_.” Kael’thas doesn’t seems sensitive to Illidan’s almost-tangible killing intent: he frowns, turns on his heels and strides to an open grimoire precariously balanced on a pile of even more books, twisting his fingers in his long hair as he does. He looks — agitated, and even more frustrated still, if that’s possible. He mutters under his breath, to low for Illidan to catch it.

 

“And what, pray tell, was it supposed to do?” Illidan crosses his arms over his chest and quirks an eyebrow, rage giving place to careful amusement.

 

Kael’thas turns his head sharply and narrows his eyes, as if to gauge if the demon hunter is messing with him or just plain stupid — which he perfectly knows he _isn’t_ , so he’s messing with him either way. “Summon a demon, of course.”

 

“A demon,” Illidan says, deadpan.

 

“Yes, _obviously_!” And, saying that, Kael’thas makes a grand sweep of his arm that shows the mess of books, chalk and candles that is his room at the moment like it’s enough of an explanation, and then goes back to his notes.

 

“Obviously,” Illidan repeats.

 

“If you’re just going to repeat everything I say and not be any help at all, Lord Illidan, you can kindly get back to your quarters.” Kael’thas hisses, in such a way that the subtext of ‘please get the fuck out of my room’ is impossible to miss. 

 

“Well, I didn’t chose to be here.” And before Kael’thas can say anything else, he asks, “Can I even get out of this circle?”

 

The question seems to drain all the anger out of Kael’thas. The mage stops in his riffling of his notes, and tilts his head to the side. “Well, there’s no reason you couldn’t — the binding only included demons, it’d be inefficient against someone any more powerful or less demonic, and if it could summon _you_ then what if it had summoned a dreadlord or something such, now _that_ would have been a disaster—” He shakes his head. “Anyway, do try— I’m sure nothing bad will happen.”

 

“How reassuring,” Illidan drawls as he steps over the lines of the circle. Nothing happens. He shrugs lightly to himself and walks to Kael’thas, looking over his shoulder. “I wasn’t aware you were also a warlock, on top of everything else.”

 

Kael’thas glances at him, now more tired than annoyed, and says, “I’m not.”

 

Illidan is very careful to keep his surprise hidden — _too_ careful, and Kael’thas, trained since early childhood to see the slightest crack in a political’s adversary mask, smiles slightly at the thought that he managed to catch the infamous demon hunter off-guard.

 

“And I suppose you haven’t found this ritual in some old, dusty grimoire lost to history?”

 

Kael’thas scoffs. “Me, using outdated magical theory? I’m not _stupid_.”

 

“That’s what I thought.” Illidan sighs and shifts his weight to his other leg, looking at the scribbled notes with renewed interest. Kael’thas's handwriting is terrible. “This is... Really advanced summoning magic.” He turns his unsettling eyes on Kael’thas. “I’d like to look into it, if you’ll allow me.”

 

“How polite of you,” Kael’thas says. “I’ll give you a copy of my notes tomorrow morning, if only you can be bothered to get to the negotiations this time.”

 

Illidan actually looks distraught at the idea. “Can’t I take those?”

 

“No, I need them to see what I did wrong. Now get the hell out of my room, Lord Illidan.”

 

The demon hunter would probably roll his eyes if he could. As it is, he only walks out with a shake of his head that makes his long hair slides over his back in a rather delightful way. Kael’thas stares, but only a little.

 

\--

 

“I think I got it this time,” Kael’thas tells Al’ar, who’s overlooking his work while very carefully not setting anything on fire. Kael’thas lightly pats his fluffy, embers-warm head with one hand as he writes adjustments on his notes with the other. The summoning array — which he’ll probably never get out of the floor, considering — has gained three extra circles (for extra security) and so many rhunes Kael’thas had to invent new ones to get what he wanted from the frustratingly old language. He’s writte them down somewhere, probably; Rommath will be happy to learn about them.

 

(They are, technically, a revolution in summoning magic, as is everything he’s been doing these last two months.)

 

“Ready?” The phoenix makes his peculiar hum-chirp of assent and Kael’thas nods. “Alright, here goes.”

 

Dawn is barely breaking — he might have forgotten to sleep, too engrossed in this new challenge. Al’ar swoops over the candles that mark the major points of the array, and the rising sun has nothing on the shimmering gold of his feathers as he lighs every single one and rises back to his perch.

 

Kael’thas smiles. He’s a familiar to his image: glorious and magnificent. 

 

He guide his chant with rhytmic gestures (it’s something he’s seen warlock do so often he wonders how he managed to forget it the first time — a rookie mistake) and slowly build a web of light around the array. It expends with the words, swirls like fallen leaves caught in the wind, golden and fel-green and colored in hues that don’t have names yet, turns into a solid sphere of bright light—

 

And then it dissipates, and in its place stands Illidan Stormrage.

 

“ _Again_?” Kael’thas says, throwing his hands up and looking at Al’ar with exasperation. The fantastical bird flaps his wings in something like a shrug and flies out the window, probably to go laugh about his failure with Rommath. Treators.

 

“I see you didn’t find the fault in your ritual,” Illidan replies with a mocking grin. 

 

Kael’thas lifts his hands and then thinks better of it and lets them fall down again. Strangling the master of the demon hunters to death is _not_ the way to go.

 

“Oh give me a _break_ , you didn’t either.” He looks pointedly at Illidan, then the door. “Now would you kindly leave me to my frustrated hair-pulling, please?”

 

“Of course, your royal highness.” Illidan steps out of the array—

 

Well.

 

Illidan _tries_ to step out of the array.

 

“You—”

 

“Improved the security measures, yes,” Kael’thas says dimly, trying his best not to laugh. 

 

A pause. “I see.” Illidan takes a deep breath and knocks on the invisible barrier with his very long, very sharp nail (claw? Talon? Kael’thas isn’t used to being turned on by things he doesn’t know the therminology of and it’s _bothering him_ ). “Would you—”

 

“Get you out of here, yes, of course, pardon me.”

 

It takes a surprising amount of time and research to get the shield down. It is, apparently, easier to keep demons _in_ than it is to get them _out,_ or at least that’s the logic of Kael’thas unique summoning ritual. 

 

It’s an opportunity to test his magic in ways he never thought about, so Kael’thas thinks he can be pardonned if, while trying to help Illidan, he throws a bunch of stuff into the array with him, to see what can enter and what is stopped by the barrier.

 

When it goes down, it frees Illidan — as well as six books of different weights and materials, a cushion, a candle, two knives, an apple core (Illidan got hungry during the hour it took to deactivate the array), a cup of tea (because Kael’thas has some manners at least) and a single sock. Living things cannot cross the threshold, as was proven by Kael’thas trying to throw a passing cat into the array and ending up with a slightly stunned and very irrate feline definitely _out_ of the array.

 

“It might have something to do with intent,” Illidan says as he scans the loose pages of notes thrown over the floor. “The first time you summoned me— What were you thinking of?”

 

“Our first meeting,” The other mage admits easily. “When Lor’themar threw me over his shoulder and almost jumped off a cliff.”

 

 “Odd. You know Theron better— for all intent and purpose, he should have been the one summoned then.”

 

“Maybe something to do with demon blood?” Kael’thas gestures to Illidan’s— well, everything. The man _does_ look rather demon-y. “This is a _demon_ summoning ritual, after all. Demon hunters are at least half demon, as far as blood is concerned.”

 

Illidan hums noncommittally. “Or maybe you’re not cut to be a warlock.”

 

And then he flees ( _makes a_ _tactical retreat_ ) the scene before Kael’thas can throw more books at him.

 

\--

 

“We need to stop meeting like this.”

 

_‘I don’t know, I kind of enjoy having you on my bedroom floor.’_

 

“You don’t say.”

 

\--

 

“Still no success on this, hm?”

 

“ _Get out of there._ ”

 

\--

 

“ _Fucking hell_!”

 

“Good morning to you too, King Sunstrider.”

 

\--

 

“I—”

 

“I will kill you with my bare hands and sends your corpse to the Legion if you say a _single word_ , Illidan.”

 

\--

 

“ _You’re supposed to be in Outland_.”

 

“Well at least we now know cross-dimensional summoning isn’t the issue.”

 

\--

 

"Still trying?”

 

“No. Here’s your paperwork. If I have to suffer through it then _so do you_.”

 

\--

 

“I wish I could find a way to summon someone else. Non-consensual teleportation holds so many possibilities.”

 

“By the Light, I hope you never do.”

 

\--

 

“I can’t believe you summoned me to the peace summit.”

 

“It wasn’t as if you’d get there yourself, hm?”

 

\--

 

“I don’t know about you or royalty in general but demon hunters, against all odds, do actually need to sleep every so often, and I was doing that _just now_.”

 

“I’m bored, come help me work on this whole summoning mess.” 

 

“Ugh, _fine_.”

 

\--

 

In the end, it’s a surprise it didn’t come bite him in the ass sooner than that.

 

Another fruitless attempt to summon an actual demon (as in: the Burning Legion kind) ends in Illidan standing in the ever-increasing array on his bedroom floor. But this time he is covered in drying blood, slightly out of breath and distinctly singed around the edge. His hairtie has been lost or broken and his hair falls freely over his shoulders, and he looks _pissed_. Also distinctly unhinged: he must be fresh out of a battle.

 

“You need to stop this,” He says as soon as he appears. 

 

“I’m _trying_ , but for some reason you keep appearing!”

 

“Then stop trying!” Illidan snarls, revealing sharp teeth and green ichor. Out of a battle against the Legion. 

 

Kael’thas bends his head and curls his fingers into his hair, pulling hard. “I’m so _close_! I can feel it! I just need to—”

 

“No.” Illidan stands to his full height and his wings opens just slightly, like a bird trying to make itself look bigger. “This has to stop.”

 

“I can’t!” Kael’thas looks up, crazed eyes and shivering hands. “I can find a way to actually summon a demon. I— _I can do it_ , I just need to keep trying!”

 

Illidan is suddenly _very_ close, breath smelling of sulfur and blood brushing over Kael’thas’s forehead as he stands above him, long black hair framing his face in darkness. “I don’t think you understand,” He says very quietly. Too calm, like a storm just before the first lightning strike. “This. _Must_. Stop. What if you had tried this an hour earlier? What if you’d taken me right out of a fight, or just before one? It’s a miracle you haven’t yet.” 

 

Poison-green blood drips from his hairline and falls on Kael’thas face. He doesn’t flinch at the burn. Instead, he grabs Illidan’s horns and drags him lower, _closer_ , and snarls right back. “I will succeed, and there’s nothing you can do to stop me.”

 

“Isn’t there?” Illidan’s voice holds a promise of pain and Kael’thas— 

 

Shivers, although he is not afraid.

 

“I could destroy you,” Illidan adds, like it’s a surprise — like it’s new. Like he never noticed that Kael’thas — bright and always burning — is smaller than he is, weaker in the way a sword is ultimately weaker than fire.

 

“You could _try_ ,” Kael’thas retorts, holding Illidan’s gaze even as his back hits the wall. He wasn’t even aware they were moving. 

 

A clawed hand fists in his hair and Illidan wrenches his head backward, barring his throat, and a second one curls around it, sharp talons brushing against his jugular. Kael’thas snaps his mouth closed and clenches his teeth around a growl, biting his tongue until it bleeds. He is better than this.

 

The horns in his hands are rugged and warm, jagged edges just sharp enough to hurt where they dig in his skin. He pulls harder and Illidan (willing or taken by surprise he cannot say, although he can guess) falls even closer. Kael’thas smiles, a predator threat of bloody teeth. 

 

And then he kisses Illidan.

 

It’s not a nice kiss, definitely not a gentle one. It’s closer to a fight, maybe, and it tastes like one, green and red blood mixing together on their lips. Kael’thas only lets go of Illidan when he’s out of breath, and he licks his lips with a feral grin.

 

“You have no power over me,” He says happily, and in a wave of his fingers Illidan is thrown back through whatever space-time rift will spit him back where he’s from.

 

He’s making progress: now that he can forces the teleportation both ways, he might find what’s keeping him from summoning anyone or anything else.

 

Whistling, Kael'thas goes back to his notes.

**Author's Note:**

> In the end, Kael'thas probably ends up summoning a _lot_ of demon hunters but never any actual demon. They get used to it.
> 
> Come to my [tumblr](https://youngster-monster.tumblr.com/) for more rambling about stuff (I realize I've been writing a lot of Kael'thas lately)

**Works inspired by this one:**

  * [Sed In Errare Perseverare...](https://archiveofourown.org/works/15177431) by [AuroraExecution](https://archiveofourown.org/users/AuroraExecution/pseuds/AuroraExecution), [w3djyt](https://archiveofourown.org/users/w3djyt/pseuds/w3djyt)




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